In a healthy shoulder joint, the head of the humerus interacts with the glenoid of the scapula to form a “ball and socket” joint. The humeral head abuts and articulates with the glenoid to provide a wide range of motion. In an unhealthy shoulder joint, the interaction between the glenoid and the humerus is compromised, requiring repair or replacement.
In some unhealthy shoulder joints, different portions of the glenoid can experience different amounts of bone erosion. For example and referring to FIGS. 1-4, a glenoid 10 may include a posterior portion 12 that has a significant amount of erosion and an anterior portion 14 that has little or no erosion. Such a glenoid is commonly referred to as a “type-B2” glenoid. As another example, a glenoid may include a supero-posterior portion that has a significant amount of erosion and an infero-anterior portion that has little or no erosion. As yet another example, a glenoid may include an infero-posterior portion that has a significant amount of erosion and a supero-anterior portion that has little or no erosion. In any of these cases, a surgeon may need to remove a significant amount of bone, specifically, cortical bone of the relatively healthy portions of the glenoid, to accommodate typical glenoid implants.
Previously, glenoid components were developed that were specifically intended to be used with type-B2 glenoids and address the issues of typical glenoid components described above. Some of these glenoid components, for example, include a scapula-facing surface in which different portions of the surface are disposed at different “elevations”. These components also include a transversely-extending surface that connects the different portions of the scapula-facing surface. These surfaces provide the glenoid component with a “stepped” appearance. However, these glenoid components nevertheless require a significant amount of bone removal and typically violate the subchondral plate. In addition, it is relatively difficult to remove bone to form an appropriately shaped surface for receiving a step-shaped glenoid component, and a surgeon must frequently insert a trial implant to check the fit with the surface.
FIGS. 5A-5C illustrate a glenoid 10 at different stages of traditional on-axis reaming. FIG. 5A illustrates a glenoid 10 with a portion of bone 11 that has deteriorated from the posterior portion 12. FIG. 5B illustrates a reamer 15 approaching the glenoid 10 along a longitudinal axis L of the glenoid 10. Portion 13 indicates the portion of bone to be removed using the reamer 15. As shown in FIG. 5C, following on-axis reaming, a significant portion 13 of the glenoid 10 has been unnecessarily removed from both the posterior portion 12 and the anterior portion 14.
As another example, FIGS. 6A-6C illustrate a glenoid 10 following off-axis reaming at different angles. Traditionally, to accomplish off-axis reaming, the entire reamer 15 is introduced into the body at an angle (i.e., 8 degrees, 12 degrees, or 18 degrees) relative to the longitudinal axis L of the bone. However, as shown in FIGS. 6A-6C, a greater portion of the anterior portion 14 is still unnecessarily removed from the glenoid 10 than is necessary for the implantation of glenoid components created for type-B2 glenoids.
FIGS. 7A and 7B illustrate yet another glenoid 10 following preparation of the bone for the insertion of a GLOBAL® STEPTECH® Anchor Peg Glenoid. In this method, a significant portion of the posterior portion 12 of the glenoid 10 has been unnecessarily removed in a stepped manner. Accordingly, there is a need for a device that minimizes the amount of bone removed.
Others of these glenoid components, for example, include a scapula-facing surface that has a constant slope. However, forces acting on the proximal or articulation surface of these components urge the sloped scapula-facing surface to slide over the prepared glenoid. This action, in turn, applies shear forces to posts or anchors that extend from the scapula-facing surface and couple to the bone. These glenoid components also present challenges to surgeons. Specifically, the reaming path for preparing the glenoid is typically across the glenoid.